Thiazolidinedione derivatives of the general formula I are described in the application WO 94/27995, 
in which
A represents a carbocyclic ring with 5 or 6 carbon atoms or a heterocyclic ring with a maximum of 4 heteroatoms in which the heteroatoms can be the same or different and denote oxygen, nitrogen or sulphur and the heterocycles can optionally carry an oxygen atom on one or several nitrogen atoms,
B denotes xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, O or S,
W denotes CH2, O, CH(OH), CO or xe2x80x94CHxe2x95x90CHxe2x80x94,
X denotes S, O or NR2, in which the residue R2 is hydrogen or C1-C6 alkyl,
Y denotes CH or N
R denotes naphthyl, pyridyl, furyl, thienyl or phenyl which is optionally monosubstituted or disubstituted with C1-C3 alkyl, CF3, C1-C3 alkoxy, F, Cl or bromine,
R1 denotes hydrogen or C1-C6 alkyl and
n denotes 1-3
as well as tautomers, enantiomers, diastereomers and physiologically tolerated salts thereof.
Compounds of the general formula I can form salts with bases since they have an acidic NH group on the thiazolidinedione ring. Suitable pharmaceutical salts are for example alkali salts such as lithium, sodium or potassium salts, alkaline earth salts such as calcium or magnesium salts, other metal salts such as e.g. aluminium salts, ammonium salts or salts with organic bases such as e.g. diethanolamine, ethylenediamine, diisopropylamine and others. The sodium salt is particularly preferred. The salts are for example prepared by treating the compounds of the general formula (I) in a known manner with a stoichiometric amount of the corresponding base.
The compounds are usually produced by a known process via alpha-halogenated carboxylic acids by subsequent synthesis of the thiazolidinedione ring system. In order to produce these carboxylic acids an aromatic amino group is diazotized and the diazonium salt is reacted with ethyl acrylate in the presence of hydrohalic acid and copper salts. This process has some disadvantages for the production of amounts on a multi-kg scale with regard to safety, upscaling, handling and synthesis complexity. For example in the reaction the aromatic amines must be diazotized to form the alpha-halogenated carboxylic acids and reacted with toxic acrylic acid ester and this reaction proceeds with unsatisfactory yields. Furthermore it is extremely problematic to apply this reaction to a larger scale for safety and environmental protection reasons.
A further production process according to the invention comprises the catalytic hydrogenation of compounds of the general formula II, 
in which A, B, W, X, Y, R, R1 and n have the meanings stated above.
However, the catalytic hydrogenation is very complicated. A poisoning of the catalyst by sulphur may occur especially for types of compound which, in addition to the sulphur contained in the thiazolidine-dione ring, carry a further sulphur atom in the molecule which leads to very long reaction periods and requires a several-fold renewal of the catalyst.
A further process for the reduction of compounds of the general formula II is known from the literature which comprises the use of magnesium as a reducing agent [e.g. C. C. Cantello et al., in J. Med. Chem. 37, 3977 (1994)].
This method circumvents the interference of the catalytic process by sulphur contained in the molecule but in the case of the aforementioned compounds of the general formula II a partial reduction of the five-membered unsaturated heterocycle occurs which leads to impurities of the desired products that are difficult to separate.
Surprisingly it has now been found that compounds of the general formula II can be smoothly reduced with a high purity by the method described last without a partial reduction of the double bonds of the five-membered heterocyclic ring system occurring if metallic aluminium is used instead of magnesium as a reducing agent, the aluminium being advantageously activated by treating the surface with salts of more noble metals.
The process can be applied in particular to a selection of particularly valuable subclasses of the general formula I which are summarized in the following under the general formula III.
Hence a subject matter of the invention is a new process for the production of compounds of the general formula (III) 
in which
A denotes CHxe2x95x90CH or S
W denotes O
X denotes S, O or NR2 in which the residue R2 is hydrogen or C1-C6 alkyl,
Y denotes CH or N
R denotes naphthyl, thienyl or phenyl which is optionally monosubstituted or disubstituted with C1-C3 alkyl, CF3, C1-C3 alkoxy, F, Cl or bromine,
R1 denotes hydrogen or C1-C6 alkyl and
n denotes 1-3
by reducing a compound of the general formula IV, 
in which A, W, X, Y, R, R1 and n have the meanings stated above with activated aluminium in a protic solvent. The surface of the aluminium can be activated by treatment with metal salts that are above aluminium in the electrochemical series. A dilute solution of mercury chloride is particularly suitable. The aluminium can be used in the form of chippings, grit or powder. Lower alcohols, in particular methanol and also water are preferably used as the protic solvent. Aprotic organic solvents that are miscible with alcohols or water can be added to improve the solubility or can be used as the major component. The reaction is carried out at 0-80xc2x0 C., preferably at room temperature or a slightly increased temperature up to 40xc2x0 C.
The invention also concerns new compounds of the general formula I which are not described in the application WO 94/27995 and which, in comparison to the compounds described in this application, exhibit a surprisingly better action profile in the treatment of diabetes mellitus. These are the following compounds:
5-{4-[2-(5-methyl-2-(thien-2-yl)-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-7-ylmethyl}-thiazolidine-2,4-dione
5-{4-[2-(5-methyl-2-(4-fluorophenyloxazol)-4-yl)-ethoxy]-benzo[b]thiophen-7-ylmethyl}-thiazolidine-2,4-dione
5-{4-[2-(5-methyl-2-(4-chlorophenyloxazol)-4-yl)-ethoxy]-benzo[b]thiophen-7-ylmethyl}-thiazolidine -2,4-dione
5-{4-[2-(5-methyl-2-(4-trifluoromethylphenyloxazol)-4-yl)-ethoxy]-benzo[b]thiophen-7-ylmethyl}-thiazolidine-2,4-dione
5-{4-[2-(5-methyl-2-(2,4-difluorophenyloxazol)-4-yl)-ethoxy]-benzo[b]thiophen-7-ylmethyl}-thiazolidine-2,4-dione
tautomers, enantiomers, diastereomers and physiologically tolerated salts thereof.
The invention in addition concerns pharmaceutical preparations which contain the compounds listed above as an active substance for the treatment of diabetes mellitus. The pharmaceutical preparations are produced and used according to conventional methods described in WO 94/27995.
The following examples are intended to elucidate the new method for the production of compounds of formula (III) without limiting the method to the said special cases. The compounds of the general formula IV are produced according to the process stated in WO 94/27995.